Abiotic control of phytoplankton blooms in temperate coastal marine ecosystems: A case study in the South Atlantic Ocean

BERMEJO, PAULA; HELBLING, E. WALTER; DURÁN-ROMERO, CRISTINA; CABRERIZO, MARCO J.; VILLAFAÑE, VIRGINIA E.

THE SCIENCE OF TOTAL ENVIRONMENT

Elsevier

Lugar: Amsterdam; Año: 2018 vol. 612 p. 894 - 902

0048-9697

Coastal waters of the South Atlantic Ocean (SAO) sustain one of the highest levels of production of the World´socean, maintained by dense phytoplankton winter blooms that are dominated by large diatoms. These bloomshave been associated to calm weather conditions that allow the formation of a shallow and well illuminatedupper mixed layer. In Bahía Engaño, a coastal site in Patagonia, Argentina (chosen as a model coastal ecosystem)winter blooms recurrently peaked on June and they were dominated almost entirely by the microplanktonicdiatom Odontella aurita. However, during the year 2015, a new wind pattern was observed - with many daysof northerly high-speed winds, deviating from the calm winter days observed during a reference period(2001-2014) used for comparison. We determined that this new wind pattern was the most important factorthat affected the phytoplankton dynamics, precluding the initiation of a June bloom during 2015 that instead oc-curred during late winter (August). Furthermore, the 2015 bloom had a higher proportion of nanoplanktoniccells (as compared to the reference period) and it was co-dominated by O. aurita and Thalassiossira spp. Othervariables such as nutrient supply and incident solar radiation did not have an important role in limiting and/orinitiating the June 2015 bloom, but temperature might have benefited the growth of small cells during August 2015. If these changes in the timing and/or the taxonomic composition of the bloom persist, they may have im-portant consequences for the secondary production and economic services of the coastal SAO.